Influence Of External Sulfate On Phosphorus Mobilization And Transformation In The Sediments Of Lake Donghu In Wuhan

A large number of pollutants have been discharged into the lakes and deposited continuously due to the anthropogenic disturbance, resulting in increasing sulfate concentration in lakes in recent decades. Eutrophication has become a global focus on water environmental problem. In this research, experiment of pilot scale with the overlying water and sediments from Lake Donghu was simulated under indoor (200L) condition to investigate the response of phosphorus on sulfate with the temperature change for almost one year. The main conclusions are as follows:(1) The physical and chemical properties of Lake Donghu varied with the input of sulfate. At the prophase of cultivation, the pH increased, while the Eh decreased. Later period of cultivation with increasing temperature, the pH of different layered sediments fell gradually, and the effect of sulfate reduction on pH decreased with the depth of the sediments. The Eh of sediments were gentle decline. Sulfate reduction was enhanced as the temperature increased. The organic matter content of sediments decreased gradually, and compared to initial values, the organic matter content of the upper, middle and lower sediments of the S500fell by31.6%,30.6%and37.5%respectively in the48th week.(2) The SO42-concentration in the overlying and pore water of S500was significantly higher than CK. The variation trend of SO42-concentration decreased with the depth of sediments. Sulfate reduction was enhanced as the temperature increased in the later period of cultivation, and the SO42-in the pore water was reduced substantially. For the S500, the SO4-concentration of the upper, middle and lower pore water in the48th week fell by80.1%,84.6%and78.3%respectively compared with the highest concentrations in the9th week. Total sulfur and elemental sulphur content in the sediments increased in the whole. Moreover, they both decreased with the increasing depth of the sediments.(3) The effect of temperature on phosphorus released from the sediments was significant. The Eh of the sediments, the SO42-concentration and organic matter decreased with the rising of temperature. Sulfate reduction intensity increased as well as elemental sulphur content, resulting in the greater ability of phosphorus release from the sediments. The concentrations of TP and SRP in the overlying water of S500, which reached maximum value by0.33mg/L and0.30mg/L in the42th week, was significantly higher than that of CK (P<0.01) and increased by91.7%and93.5%respectively compared to initial value. (4) In the later period of cultivation, there was a negative relationship between organic phosphorus and organic matter in the sediments. Organic phosphorus in the sediments were hydrolyzed and transformed to inorganic phosphorus under the action of phosphatase, and its content decreased gradually. Sulfate input caused higher activity of phosphodiesterase than phosphomonoesterase in the sediments. With the increasing of temperature, the activity of phosphatase was enhanced. As a result, the release of internal phosphorus in the sediments into the overlying water was promoted.(5) The SRB amounts decreased with the increasing depth of the sediments. The SO42-of the water was consumed due to the reduction and respiration effect of SRB under the anaerobic conditions. The organic matter was oxidated and decomposed in the sediments simultaneously, resulting in the gradually decrease of its content. The amount of organic phosphorus solubilizing microorganisms was higher than inorganic ones in the sediments. There was a negative relationship between the amount of phosphate solubilizing microorganisms and the content of TP in the upper sediments.